GO-2026-6911
SSRF and credential leak via unvalidated Location header in github.com/mark3labs/mcp-go
GO-2026-6911 is a vulnerability with no CVSS score yet in github.com/mark3labs/mcp-go, published November 5, 2026. No source lists public exploit code. No source names a fixed version.
- Severity
- UnratedNo CVSS score yet
- Exploit chance
- UnscoredNo EPSS score yet
- Exploitation
- None knownNot on CISA’s or ENISA’s lists
- Fixed in
- No fix listedNo source names one
Description
In github.com/mark3labs/mcp-go/client/transport, NewStreamableHTTP constructs an http.Client with a nil CheckRedirect policy when no custom WithHTTPBasicClient is supplied, and attaches static custom headers and OAuth bearer tokens inside a RoundTripper layer. If an MCP server responds with a 3xx redirect, the client follows the Location header to arbitrary hosts and schemes and attaches configured WithHeaders and OAuth Authorization headers to the redirected request, enabling server-side request forgery (SSRF) and credential disclosure.
Affected packages
| Package | Affected | Fixed |
|---|---|---|
github.com/mark3labs/mcp-goGo | All versions | None known |
What each source reports
OSVNo score
SSRF and credential leak via unvalidated Location header in github.com/mark3labs/mcp-go
In github.com/mark3labs/mcp-go/client/transport, NewStreamableHTTP constructs an http.Client with a nil CheckRedirect policy when no custom WithHTTPBasicClient is supplied, and attaches static custom headers and OAuth bearer tokens inside a RoundTripper layer. If an MCP server responds with a 3xx redirect, the client follows the Location header to arbitrary hosts and schemes and attaches configured WithHeaders and OAuth Authorization headers to the redirected request, enabling server-side request forgery (SSRF) and credential disclosure.
- Record
GO-2026-6911- Updated
- 2026-11-06
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.